Known in the art is a method for measuring pressure by applying a reference voltage to the input of a piezoelectric sensor and determining the transformation ratio of the sensor depending on the pressure applied thereto during operation at a resonance frequency (SU A1 317,931).
Also known in the art is a method for monitoring the physical parameters of a liquid, comprising generating oscillations in the medium being monitored and receiving signals passing therethrough and determining the pressure from their characteristics (SU A1 456,996).
Known in the art is an apparatus for ultrasonically monitoring biological liquids, comprising a casing having a through conduit containing a measuring chamber and ultrasonic oscillation transducers provided coaxially at the opposite walls thereof (SU A1 932,389).
The drawbacks of the prior art methods and apparatuses are a low sensitivity and accuracy of measurement, which makes them unsuitable for use within a wide range of pressures and temperatures because of the non-rigid attachment of the ultrasonic oscillation transducers between the ends of the casing and the covers due to resilient spacers being inserted between the unstrained surface of the piezoelectric transducers and the mounting components.
The low accuracy of measurements is also due to the fact that the electrodes on piezoelectric plate surfaces unstrained by the medium under investigation do not coincide with the diameter of the measuring chamber, which results in the propagation of ultrasonic waves within the casing of the measuring chamber as well as in the medium under investigation.